Developing and debugging zxdb

Run tests

To run the zxdb tests:

fx test zxdb_tests

To run the debug_agent tests:

fx test debug_agent_unit_tests
fx test debug_agent_integration_tests

Reload debug_agent.cm after a new version is built

Since debug_agent_launcher is a long-running process, the system will not try to update the debug_agent package after the first ffx debug connect invocation. To force the system to unload debug_agent.cm, use

ffx component stop /core/debug_agent

Enable debug logging in debug_agent

Adding --select core/debug_agent#DEBUG to fx log will enable the debug logging of the debug_agent, e.g.

fx log --select core/debug_agent#DEBUG --tag debug_agent --hide_metadata --pretty

Enable debug logging in zxdb

To enable debug logging in zxdb, use

ffx debug connect -- --debug-mode

Launch zxdb in another debugger

It's possible to ask ffx debug to launch zxdb in another debugger, e.g. lldb.

ffx debug connect --debugger lldb

This command will bring the lldb shell and you can use "run" to start the zxdb.

The "lldb" in the command can be substituted by "gdb". However, using gdb might bring several issues including

  • Older versions of gdb may not support all DWARF 5 standard, and some information might be missing such as source file listing.
  • Ctrl-C will not bring you back from zxdb to gdb. A workaround is to use pkill -INT zxdb in another window to stop the zxdb.

Debug debug_agent in another debug_agent

It is also possible to attach a debug_agent to another debug_agent. This is done frequently by the debugger team.

// Run the debugger that will attach to the "to-be-debugged" debug_agent.
$ ffx debug connect

// Within zxdb.
[zxdb] attach debug_agent
Waiting for process matching "debug_agent".
Type "filter" to see the current filters.
Attached Process 1 state=Running koid=345223 name=debug_agent.cm
Attached Process 2 state=Running koid=345403 name=/pkg/bin/debug_agent
// The first debug_agent will capture the launcher and itself. Detach to avoid any deadlock.
[zxdb] pr 1 detach
[zxdb] pr 2 detach
// Create a breakpoint on $main
[zxdb] break $main

// Launch another debugger in another window
$ ffx debug connect

// * Within the first zxdb:
Attached Process 1 state=Running koid=12345 name=/pkg/bin/debug_agent
Breakpoint 1 now matching 1 addrs for $main
🛑 process 1 on bp 1 main(int, const char**) • main.cc:101
    99
   100 int main(int argc, const char* argv[]) {
 ▶ 101   debug_agent::CommandLineOptions options;
   102   cmdline::Status status = ParseCommandLine(argc, argv, &options);
   103   if (status.has_error()) {

// Now you have two running instances of the debugger!